Liquid anode electrochemical cell

ABSTRACT

An electrochemical cell is provided which has a liquid anode. Preferably the liquid anode comprises molten salt and a fuel, which preferably has a significant elemental carbon content. The supply of fuel is preferably continuously replenished in the anode. Where the fuel contains or pyrolizes to elemental carbon, the reaction C+2O 2− →CO 2 +4e −  may occur at the anode. The electrochemical cell preferably has a solid electrolyte, which may be yttrium stabilized zirconia (YSZ). The electrolyte is connected to a solid or liquid cathode, which is given a supply of an oxidizer such as air. An ion such as O 2−  passes through the electrolyte. If O 2−  passes through the electrolyte from the anode to the cathode, a possible reaction at the cathode may be O 2 +4e − →2O 2− . The electrochemical cell of the invention is preferably operated as a fuel cell, consuming fuel and producing electrical current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/134,555, filed May 19, 2005, which claims priority under 35 U.S.C. §119(e)(1) to Provisional U.S. Patent Application Ser. No. 60/572,900,filed May 19, 2004. The disclosures of which are incorporated byreference in their entirety.

TECHNICAL FIELD

This invention relates generally to electrochemical cells, andspecifically to electrochemical cells capable of operation as fuelcells, using directly fuels other than hydrogen.

BACKGROUND

A typical device for direct (one-step) conversion of chemical energyinto electricity utilizes fuel and oxidizer as reagents. Both reagentsmay be in gas, liquid, or solid (including paste) forms.

Batteries are electrochemical devices that irreversibly consume thereagents while supplying current to an external circuit. Rechargeablebatteries are devices that reversibly consume the reagents, such thatthe initial reagents may be restored by supplying a current to thedevice from an external source. The major limitation of all batteries istheir limited capacity, usually expressed in Ampere-hours. Rechargeablebatteries have a limited number of charge-discharge cycles and thuseventually fail.

The fuel cell is another type of electrochemical device for generatingelectricity. Fuel cells are characterized by having open anode andcathode reaction chambers. Fuels cells operate when fuel is suppliedinto the anode chamber and oxidizer is supplied into the cathodechamber. Fuel cells do not have such disadvantages as limited capacityand a limited number of charge-discharge cycles. The efficiency of theelectrochemical fuel cell increases with temperature for the practicaltemperature ranges. Typical fuel cells may have electric outputs rangingfrom under 1 kW up to megawatts.

Schematically, a fuel cell may be described as a multi-layer system:fuel/current collector/anode/electrolyte/cathode/currentcollector/oxidizer. A typical solid oxide fuel cell operating onhydrogen may be described as hydrogen/nickel cermet/yttria stabilizedzirconia/lanthanum strontium manganite/air. Current collectors areembedded in the anode and cathode.

A major disadvantage of conventional fuel cell design is that theelectrode reactions proceed using an inefficient three-phase boundary.To elaborate, the fuel cell electron flow is generated by anelectrochemical reaction of fuel oxidation with release of electrons.Conventional oxidation reactions proceed at a three-phase boundary:electrode-electrolyte-gaseous reactant. The actual working surface ofthe electrodes in this case is very small and does not exceed 1-4% ofthe apparent electrode surface. Accordingly, more than 95% of theelectrode area does not participate in the electricity generationprocess. Multiple attempts have been made to increase the useful area ofthe electrodes by introducing mixed (electronic and ionic) conductorsinto the three-phase boundary. When this is done, working area mayincrease up to 5-10%. Still, at best, about 90% of the electrode area isnot being used.

Fuel cell developers devote major attention to cells operating ongaseous fuel (hydrogen, natural gas, CO). Cells operating on a solidfuel, such as carbon-containing materials (coal, biomass, or waste—bothmunicipal and from the petrochemical industry) have received much lessattention. At the same time, operation on solid fuel may have suchadvantages as: much safer operation (fuel is not flammable orexplosive), easier transportation, generally low cost, high powerdensity, and, in some cases such as when carbon-containing fuel is used,much higher efficiency of energy conversion. The last is a result of thenear-zero entropy loss in complete electrochemical oxidation of carbon.This translates to efficiency above 70%, while the efficiency ofgas-fueled cells is in the 30-50% range.

Use of carbon-containing fuel for electricity generation inelectrochemical fuel cells (Direct Carbon Fuel Cell or DCFC) opens anopportunity to eliminate release of fuel oxidation products andcontaminants into atmosphere, which is the major problem associated withcoal combustion power plants.

For general background on fuel cells, please refer to James Larminie &Andrew Dicks, Fuel Cell Systems Explained (Wiley 2d ed. 2003), and toEG&G Services et al., Fuel Cell Handbook (U.S. Department of Energy, 5thed. 2000).

A variety of schemes have been proposed for a direct carbon fuel cell.None have as yet come to commercial fruition. For example, U.S. Pat. No.5,298,340 to Cocks and LaViers stated that “[t]hermodynamic factorsfavor a solid carbon fuel cell over other fuel cell designs.” Theyproposed “the dissolution of carbon into a solvent” which would “act[ ]as an anode.” In their subsequent U.S. Pat. No. 5,348,812, Cocks andLaViers taught that “[f]uel cells containing an anode of molten metalinto which carbon has been dissolved, and a carbon-ion electrolyte, canbe improved by making the molten metal the same as that used as thecation on the solid carbon-ion-electrolyte.”

U.S. Pat. No. 6,607,853 to Hemmes discusses fuel cells based on theoxidation of carbon and carbon-containing materials contained in amolten corrosive salt. The possibility of internal reformation isincluded, but not explicitly required. In Hemmes' disclosure the moltencorrosive salt contacts both the solid electrolyte and the anode. Hemmesdiscloses that the anode may be porous, made of nickel, and in contactwith the solid electrolyte. Hemmes also discloses that the anode may bepositioned at a distance from the solid electrolyte.

U.S. Pat. No. 6,692,861 to Tao addresses a fuel cell with acarbon-containing anode and an electrolyte having a melting temperatureof between about 300° C. and about 2000° C. in contact with the anode.U.S. Pat. No. 6,200,697 to P. Pesavento of SARA, Inc., Cypress, Calif.,describes a concept for generating electricity using a carbon-containingconsumable anode. Because that concept employs a consumable anode, it isin essence a large nonrechargeable battery. Subsequently, J. Cooper ofLawrence Livermore National Laboratory has sought to develop a fuel cellemploying carbon nanopowder as fuel using molten carbonate electrolyte,similar to the concept developed by Robert D. Weaver at SRIInternational in the 1970s.

There is thus a need in the art for a direct carbon fuel cell which canbe scaled up effectively to a commercially viable size, at a minimum tothe hundreds of kilowatts of present-day commercial phosphoric acidcogeneration fuel cell plants or molten carbonate fuel cells, and whichcan operate efficiently with naturally available fuels such as coal,coke, tar, biomass, and various forms of carbon-containing wastes.

SUMMARY OF THE INVENTION

The patent describes fuel cells for converting fuel chemical energy intoelectricity. The concept is based on the replacement of the traditionalthree phase reaction boundary (electrode-gas-electrolyte) with atwo-phase boundary concept: liquid electrode(s) mixed with fuel oroxidizer separated by a solid electrolyte.

A preferred embodiment of the invention includes a fuel cell whichcomprises an electronic conductor serving as an anode current collector,a liquid anode, a fuel distributed in the liquid anode, a solid oxygenion-conductive electrolyte, a gas diffusion cathode, an inlet forgaseous oxidizer, and an outlet for gas evolved during the operation ofthe fuel cell.

A further preferred embodiment of the invention interconnects a numberof fuel cells in order to obtain higher voltage and power. An electricalload, for example an DC/AC inverter, having two terminals is connectedwith one terminal connected to the anode current collector of the firstfuel cell and the other terminal connected to the cathode currentcollector of the last fuel cell. Fuel cells may also be connected inparallel or in series and in parallel.

A further preferred embodiment of the invention is a method forsupplying an electric current to a load. Fuel is mixed with a conductiveliquid anode. The fuel may be, for example, a carbon-containing material(coal, coke, biomass, tar, or various waste forms) or a metal (forexample aluminum) in a powder form. The electronically conductivemixture of the liquid anode with fuel contacts a solid oxygenion-conductive electrolyte. The fuel is oxidized by oxygen ions enteringthe liquid anode from the electrolyte, releasing electrons. An oxidizeris supplied to a cathode connected to the opposite side of solidelectrolyte, causing an oxygen reduction reaction to occur to produce aflux of oxygen ions through the electrolyte. The liquid anode iselectrically connected to a terminal of the load via an electronicallyconductive current collector. With this method executed in a preferredmanner as discussed below, the current supplied will be sufficient totransfer to the load at least 100 mW for each square centimeter of cellworking surface area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general schematic diagram of a liquid anode electrochemicalcell.

FIG. 2 is a schematic design for a liquid anode electrochemical cell.

FIG. 3 illustrates a continuous operation liquid anode fuel cell in afurther embodiment of the present invention.

FIG. 4 illustrates a fuel cell stack assembly formed of a number of fuelcells having liquid anode and cathode.

FIG. 5 shows cell power density as a function of current density for anelectrochemical cell of the invention.

FIG. 6 shows cell power density as a function of temperature for anelectrochemical cell of the invention operating with coal, biomass, andtar.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Before describing the present invention in detail, it is to beunderstood that this invention is not limited to specific fuels,materials, or device structures, as such may vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include both singularand plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “an outlet” includes a plurality ofoutlets as well as a single outlet, reference to “an inlet” includes aplurality of inlets as well as single inlet, and the like.

The present invention introduces electrochemical devices forelectrochemical energy conversion, which are believed to have two-phasereaction zones. A two-phase reaction zone for oxidation reactions isestablished by using a liquid anode. A two-phase reaction zone forreduction reactions is established by using a liquid cathode.

One embodiment of the present invention teaches a liquid electrode fuelcell having a solid electrolyte with a gas diffusion cathode on oneside, and a liquid anode on the other side. The liquid anode iselectronically conductive media, based, for example, on molten saltsmixed with electronically conductive fuel particles. The liquid anodealso plays the role of the fuel carrier. The liquid anode may bestagnant or it may recirculate through the fuel cell constantlysupplying fuel and removing fuel oxidation products and fuel impurities.Electronic conductivity of the liquid electrode makes the currentcollection scheme much more efficient because the liquid electrode actsas if it were a part of a distributed current collector.

In fuel cells of the invention with a liquid anode, the anode will tendto conduct electrons reasonably well. Thus, the electrochemical reactionwill take place at the boundary between the liquid anode mixed with fueland an oxygen ion conducting electrolyte (a two-dimensional “two-phaseboundary”). In the case of an ionically conductive liquid anode, thatreaction zone may be expanded to the bulk of the liquid anode (athree-dimensional reaction zone). If the fuel is a finely dispersedsolid within the liquid anode, the electrochemical reaction can takeplace at a large surface area. As a result, the liquid anode fuel cellwill have higher power density and will be able to generate moreelectricity while having smaller geometrical dimensions. A liquidelectrode fuel cell will scale up to hundreds of kW or even tens of MWof electric output more easily than conventional fuel cells with athree-phase reaction boundary, such as Solid Oxide Fuel Cells (SOFC).

Similar advantages in terms of reaction area may be obtained for thereduction of oxygen if the cathode is an ionic liquid.

There are other technical, manufacturing, and operating advantagesbesides a large reaction area to having one or both of the electrode(s)in an electrochemical system be liquid. From a heat transferperspective, a liquid anode carrying solid fuel will tend to have muchhigher heat capacity than gaseous fuel, reducing heat differentials andallowing efficient transfer of heat generated in the electrochemicalsystem. Liquids do not raise the same concerns with thermal expansionmismatch that solid electrodes do, and so there may be longevityadvantages to the use of liquid electrodes. Recirculation of the liquidanode provides a means to achieve close to complete utilization of thefuel. It is also simpler with liquid anode fuel cells to provide an exitpath for the gases evolved and reduce accumulation of impurities. Incontrast, in gas-fueled cells, fuel oxidation gases will dilute theincoming fuel stream so that portions of the fuel cell which aredownstream in the anode gas flow may be comparatively poorly suppliedwith fuel, adversely affecting efficiency.

A fuel oxidation reaction which has a high reaction surface area in aliquid anode can run without catalyst. This is an important positiveattribute for liquid anodes because commonly available fuels such ascoal and biomass may contain impurities that would poison a catalyst.

Sealing requirements to separate fuel and oxidizer are not so stringentas in the case of gas fueled cells, which helps achieve low cost,reliability, and scalability.

The fuel cells of the invention may be operated with static orflow-through modes of operation.

In a static mode of operation, the liquid electrolyte (or liquid/solidcomposite electrolyte/electron-conductor/fuel) undergoes no net motionduring cell operation. Stirring may be used, however, to facilitateparticle-particle and/or particle-electrode contact, enhance diffusionalmass transport, or to dislodge trapped gas bubbles. Furthermore, theliquid anode may be periodically drained to remove suspended anddissolved impurities, and replaced with fresh liquid.

In a flowing mode of operation, liquid anodes and/or cathodes are causedto flow during cell operation. The flow may be gravitationally inducedfrom an upper reservoir to a lower. Alternatively the fluid can bepumped in a continuously recirculating flow down, along, or up throughthe cell. The purpose of the flow may be to enhance diffusional masstransport, to dislodge trapped gas bubbles or to remove suspended anddissolved impurities in continuous recirculation.

The electrochemical devices of the invention may be, for example, oftubular, planar, or monolith configurations.

FIG. 1 depicts in schematic form an exemplary configuration of theliquid anode concept of the invention. The liquid anode 10 contains fuelparticles depicted as black circles 12. The liquid anode also containsgases evolved by the anode reaction, depicted as bubbles 14. Immersedwithin the liquid anode is an anode current collector 16. O²⁻ ions passthrough electrolyte 20 entering the liquid anode 10. On the other sideof electrolyte 20, there is a cathode 24. It is in contact with acathode current collector 26. Passing over the cathode is gaseousoxidizer 28, which is reduced at the cathode creating the O²⁻ ions.

A preferred embodiment of the invention includes a fuel cell whichcomprises an electronic conductor serving as an anode current collector,a liquid anode, a fuel distributed in the liquid anode, a solid oxygenion-conductive electrolyte, a gas diffusion cathode, an electronicconductor serving as a cathode current collector, an inlet for gaseousoxidizer, a second inlet for replenishing or recirculating the liquidanode, an outlet for used gaseous oxidizer, with an optional secondoutlet for recirculating fuel and gas evolved during the operation ofthe fuel cell.

In the normal operation of such a fuel cell, the two terminals of anelectrical load are connected to the anode current collector and thecathode current collector. Preferably, a number of such fuel cells wouldbe interconnected, with one terminal of the electrical load connected tothe anode current collector of the first cell and the other terminalconnected to the cathode current collector of the last cell. Theelectrical load will typically include a DC/AC converter.

The anode current collector may be any suitable metal or otherelectronic conductor compatible with the conditions of use. Preferablythe anode current collector is in the form of a mesh or a spiral.Alternatively, the anode current collector may have a solid shapedefining channels in which the liquid anode exists. The channels mayserve to channel the liquid anode when it recirculates.

The liquid anode is any liquid which is electronically conductive whenmixed with fuel particles and compatible with conditions such asoperating temperatures. Preferably the liquid anode is a composition ofmolten salts and molten oxides. Examples of suitable salts includeeutectic mixtures of K₂CO₃, Li₂CO₃, and/or Na₂CO₃.

It is preferred that the liquid anode containing fuel be recirculatedusing natural circulation or a pump. Such recirculation has, forexample, the benefit that it achieves a more uniform distribution of thefuel within the liquid anode.

Suitable solid fuels, for example, are those containing carbon, whichundergoes the reaction C+2O²⁻→CO₂+4⁻e given a suitable supply of O²⁻ anda suitable sink for electrons e⁻ or metals, such as aluminum.

Usable fuels containing carbon can be, for example, coal, coke, tar,biomass, and plastic waste. Preferably the fuel comprises solidparticles.

The concentration of fuel in the liquid anode will vary over time as thefuel cell is operated and fuel is consumed and replenished. The choiceof fuel concentration can influence the efficiency of the fuel cell. Asit was observed experimentally, anode ohmic losses can be reducedsignificantly by a higher concentration of fuel.

The electrolyte may be selected from a group of solid oxide oxygen ionconductive materials, stable in the expected operating conditions, andcan be fabricated in the form of thin layers on a supporting substrate.Among suitable electrolytes are ytrria-stabilized zirconia (YSZ) andlanthanum gallate with doping of the lanthanum sublattice with strontiumfrom about 0% to about 30% and of the gallium sublattice with lithiumoxide from about 0% to about 30%. Additives, such as alumina, may beincluded in modest quantities to stabilize the electrolyte further.

In a preferred embodiment, the electrolyte may be a thin filmelectrolyte with thickness of, for example, 1-50 microns deposited on asupporting cathode. Alternatively, it may be a self-supporting solidelectrolyte with thickness, for example, up to 0.3-0.8 mm.

The cathode may be any suitable gas permeable mixed conductive materialwith the coefficient of thermal expansion (CTR) compatible with the CTRof the electrolyte. The cathode may be of the type referred to as “gasdiffusion” cathodes. A preferred cathode is strontium doped lanthanummanganite.

In an alternative embodiment of the invention, the cathode may be anionic liquid carrying oxidizer.

The cathode current collector is an electronically conductive materialsuch as metal or alloy stable under given oxidizing conditions. Thecathode current collector preferably contacts the cathode at a number ofpoints. When the cathode current collector is metallic, a mesh or aspiral are preferred shapes of the cathode current collector.

A preferred oxidizer is air.

The fuel cell is enclosed in a vessel of a suitable material adapted tothe conditions of operation. A number of geometric arrangements of thefuel cell are possible. The common arrangement for fuel cells is as alarge number of planar or tubular fuel elements which are connectedtogether into a “stack.”

The temperatures employed in fuel cells of the invention, in order tocause the anode and cathode reactions to proceed a desirable rate, meanthat the gases leaving the fuel cells (for example CO₂ where the anodereaction is C+2O²⁻→CO₂+4e⁻) will contain considerable usable thermalenergy. The operation of the fuel cell will evolve heat, for examplethrough ohmic loss, which will be transmitted to the gases as well as tothe liquid anode. In such an arrangement preferably the heat of theexiting gases would be made use of in some way. It could be conveyed toother fluids, for example incoming oxidizer, water needing to be heated,or fluid to be used for heating a structure, by means of a heat exchangemechanism. The use of the heat of the exiting gases or, in some cases,the heat of the circulating liquid anode, would permit the fuel cells ofthe invention to be used in a combined heating and power plant, in themanner that existing phosphoric acid, molten carbonate electrolyte, andsolid oxide fuel cells are employed.

There is considerable concern with CO₂ emissions into the atmospherebased on the belief that they give rise to a greenhouse effect whichwarms the earth. The CO₂ produced where the anode reaction isC+2O²⁻→CO₂+4e⁻ is therefore readily confined and may be sequestered insome manner or utilized further, for example in the cathode gas streamof a conventional hydrogen fuelled molten carbonate electrolyte fuelcell. The relative purity of the CO₂ produced when the anode reaction isC+2O²⁻→CO₂+4e⁻ facilitates its sequestration.

In the fuel cells of the invention it is possible to provide fuel in acontinuous or batch fashion to the liquid anode. In some cases it may bepossible to replenish the fuel periodically in a batch fashion throughan inlet giving access to the liquid anode. It may also be desirable,when naturally occurring fuels such as biomass are used, to remove fromthe liquid anode unreacted residue of the fuel. Furthermore, gasesgenerated by the anode reaction and fuel impurities may evolve ordissolve in the liquid anode material and have to be removed to preventcontamination of the liquid anode. For these purposes, it is preferredthat the circulation of the liquid anode material be such that somefraction of that material is at a location where it can conveniently beaccessed for purposes of replenishment or, if desired, removal of fuelresidue and/or dissolved gases.

In a particularly preferred embodiment of the invention, the fuel is aground solid, for example carbon, coal, wood, or aluminum. The anode isa liquid, for example a eutectic mixture of suitable molten salts. Theanode current collector is a metal member immersed in the liquid anodeand adjacent to the surface of solid electrolyte. The electrolyte is anO²⁻ conducting solid, for example yttria-stabilized zirconia. Thecathode is a suitable porous mixed conductor, for example lanthanumstrontium manganite. The cathode current collector is a metal membercontacting the cathode at a considerable number of points. The operatingtemperature is between 600° C. and 1000° C.

FIG. 2 depicts a configuration of this preferred embodiment used tostudy experimentally the performance of the liquid anode fuel cell. Asmay be seen, a tubular arrangement was adopted, with the platinum anodecurrent collector 48 and liquid anode 40, which comprises a moltenmixture of Li₂CO₃+K₂CO₃+Na₂CO₃, enclosed by a containing tube 50. Thesolid YSZ electrolyte closed end tube with wall thickness 0.3-0.8 mm 42is immersed into the anode, and the LSM cathode 46 is deposited as a 1mm layer on the inner surface of the solid electrolyte tube. The cathodecurrent collector 49 lies inward of the cathode itself. The tubecontaining the fuel cell is closed on both ends. Air is supplied throughthe inner portion of the tube 45 and exhausted through a concentric tube44. A version of FIG. 2 has been constructed with a YSZ tube diameter 10mm, the height of the cathode 10 mm, and employing a containing tubeinner diameter of 27 mm.

FIG. 3 illustrates a continuous operation fuel cell 500 in a furtherembodiment of the present invention. The fuel cell 500 includes liquidelectrodes 502 and 504 equipped with current collectors (not shown)separated by a solid ion conductive electrolyte 506, a fuel dispensingmodule 508, oxidizer supplying module 510, a module for separation ofthe reaction products 512, an anode circulation module 514 (e.g., apump), a cathode circulation module 516, and two heat exchangers 518 and520.

FIG. 4 illustrates a fuel cell stack assembly 550 having a plurality ofliquid electrode planar fuel cells 552 according to a differentembodiment of the present invention. It is seen that both anode andcathode are liquid in this embodiment, and that the respective anode andcathode current collectors form channels for the flow of the liquids.The liquid electrodes are circulated by means of one or moreelectrically insulated pumps (not shown) in order to establish a uniformdistribution of fuel and oxidizer over the reaction zone.

FIG. 5 depicts power density as a function of current density for thefuel cell shown in FIG. 2 at 950° C. with PRB coal as fuel. Volumetricfuel content in the liquid anode was about 40%. An electromotive forceof about 1.4 V was observed in this experiment. A maximal power densityabove 100 mW/cm² was observed. This level of power density achieved withreal fuel suggests that the inventive fuel cell has considerablecommercial potential, as one may conclude from comparison withcommercially available molten carbonate fuel cells, which have poweroutputs above 100 kW and power densities close to 100 mW/cm². (As isnormal in describing fuel cell operation, power density was obtained inFIG. 5 dividing power by cell working surface area. For theconfiguration of FIG. 2, this working surface area is the area of acylinder with diameter equal to the outer diameter of the YSZ tube. Theheight of the cylinder is the minimal height among the cathode, cathodecurrent collector, and anode current collector.)

FIG. 6 depicts the peak power density as a function of operatingtemperature observed at similar conditions for coal and other realfuels—biomass (pine saw dust) and tar (Maya atmospheric tower bottom)with the preferred fuel cell shown in FIG. 2 and described above.

It is contemplated that fuel cells of the invention will beinterconnected and assembled in a stack. Sufficient number of stackswill be interconnected to achieve desired power output from a standaloneunit. The modular principle and the resulting scalability are anattractive feature of the invention. For example, this plant couldproduce hundreds of kilowatts as a distributed power generation unit orbe scaled up to tens of megawatts for centralized power generation.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, that theforegoing description and the examples that follow are intended toillustrate and not limit the scope of the invention. Other aspects,advantages, and modifications within the scope of the invention will beapparent to those skilled in the art to which the invention pertains.

All patents, patent applications, and publications mentioned herein arehereby incorporated by reference in their entireties. However, where apatent, patent application, or publication containing expressdefinitions is incorporated by reference, those express definitionsshould be understood to apply to the incorporated patent, patentapplication, or publication in which they are found, and not to theremainder of the text of this application, in particular the claims ofthis application.

1. A fuel cell comprising (a) a conductor serving as an anode currentcollector, (b) a liquid anode, (c) fuel distributed in the liquid anode,(d) a solid oxygen ion-conductive electrolyte, (e) a solid gas diffusioncathode, (f) a first inlet for gaseous oxidizer, (g) an outlet for gasevolved during the operation of the fuel cell.
 2. The fuel cell of claim1, further comprising an anode recirculation system for recirculatingthe liquid anode.
 3. The fuel cell of claim 1, further comprising a fuelreplenishment system for replenishing the supply of fuel in the liquidanode.
 4. The fuel cell of claim 1, further comprising a liquid anodecleanup system for removing from the liquid anode fuel oxidationproducts and impurities accumulated during cell operation.
 5. The fuelcell of claim 1, wherein the anode current collector forms a channel forthe passage of the liquid anode.
 6. The fuel cell of claim 1, whereinthe fuel is selected from one of carbon-containing materials, a metal,or hydrocarbons.
 7. The fuel cell of claim 6, wherein the fuel comprisestar, elemental carbon, coal, coke, biomass, carbon-containing waste, oraluminum.
 8. The fuel cell of claim 1, wherein the fuel is solid.
 9. Thefuel cell of claim 8, wherein the fuel is in the form of solidparticles.
 10. The fuel cell of claim 1, wherein the fuel is a liquid ormolten hydrocarbon.
 11. The fuel cell of claim 1, further comprising asystem for confining some or all of the gases evolved during theoperation of the fuel cell so as to avoid their dispersal into theatmosphere.
 12. The fuel cell of claim 1, comprising a liquid anodeoutlet which is connected to a heat exchanger for utilizing the heat inliquid anode and gaseous fuel oxidation products leaving the fuel cell.13. The fuel cell of claim 1, further comprising a second outlet forused oxidizer gases, wherein the second outlet is connected to a heatexchanger for utilizing the heat in the used oxidizer gases leaving thefuel cell.
 14. The fuel cell of claim 1, wherein a power density of atleast 50 mW/cm² can be obtained using coal and coke as a fuel.
 15. Thefuel cell of claim 1, wherein a power density of at least 35 mW/cm² canbe obtained using biomass, tar, carbon-containing waste, or a metal as afuel.
 16. The fuel cell of claim 1, wherein a power density of at least50 mW/cm² can be obtained using acetylene black as a fuel.
 17. The fuelcell of claim 1, wherein the liquid anode comprises molten salts, moltenoxides, or mixtures thereof.
 18. The fuel cell of claim 17, wherein theliquid anode comprises alkali salts.
 19. The fuel cell of claim 1,wherein the liquid anode mixed with fuel is electronically conductive.20. The fuel cell of claim 1, wherein the liquid anode is oxygen ionconductive.
 21. A process for supplying electric current to a loadhaving terminals, comprising the steps of: (a) mixing fuel with a liquidanode, (b) causing the liquid anode to contact a solid oxygenion-conductive electrolyte, (c) causing the fuel to react with oxygenions entering the liquid anode from the electrolyte, releasingelectrons, (d) collecting released electrons via an anode currentcollector, (e) supplying an oxidizer to a cathode connected to the solidelectrolyte, (f) causing a reduction reaction to occur at the cathode bysupplying electrons via cathode current collector, thus producing oxygenions which move through the electrolyte, (g) electrically connecting thecathode and liquid anode current collectors to terminals of the load,wherein the current supplied is sufficient to transfer energy to theload at a cell power density of 50 mW/cm².